I know the ink prices have been kicked around more then just a little, but.. $1195 for the P900 and $1795 for the P5000, only $600 difference and it is twice the printer quality.
Then comes the ink P900 is .84 per ml and the P5000 ink is .45, almost half the cost.
If you use a 1000ml of ink a year the savings with the P5000 is $390 just in 1 year. 2 years your savings are $780 and you have paid for the upgrade to the P5000 just in ink savings.